Editing Scheme in the installation image

[Ludovic Courtès]

Hello Guix!

One issue that’s often reported is that it’s inconvenient to edit the
config file with all its parentheses in the installation image given the
available options (Zile, Nano, and nvi).

Something like Paredit and ‘show-paren-mode’ in Emacs would help avoid
mistakes such as unbalanced parenthesis.  However ‘emacs-minimal’ takes
180 MiB and it would be unreasonable to include it.

So I figured we could use Zile-on-Guile¹ (yes!) and extend it to have
something that resembles Paredit, like:

;; Poor developer’s Paredit.

(define (paredit-open-paren)
  (insert "()")
  (backward-char))

(define (paredit-close-paren)
  (unless (search-forward ")")
    (insert ")")))

(set-key "(" 'paredit-open-paren)
(set-key ")" 'paredit-close-paren)

Of course, it takes more than these few lines to write a real Paredit,
but still, wouldn’t it be cool?  :-)

What do people (Mike in particular!) think?

Ludo’.

¹ https://www.gnu.org/software/guix/packages/z.html#zile-on-guile

PS: The closure of Zile-on-Guile is 103 MiB, but Zile-on-Guile itself is
    only 400K and its dependencies are already in the installation
    image.